UNITED NATIONS -- An accomplished former U.S. prosecutor has filed a grievance accusing Secretary-General Ban Ki-moon of blocking his hiring to the U.N.'s top investigative post because of discrimination based on gender and nationality.

The dispute over Robert Appleton's appointment is the latest salvo in a high-stakes fight within the world organization over how to fix the U.N.'s long-troubled internal watchdog agency. U.N. associate spokesman Farhan Haq said Wednesday that Ban's office could not comment on matters before the tribunal.

Appleton's 76-page application to the U.N. Dispute Tribunal, a copy of which was obtained by The Associated Press, said that Ban's refusal to hire him is a breach of the U.N. Charter and General Assembly resolutions.

He is seeking $1 million in damages and up to about $500,000 in lost wages and benefits.

Appleton headed the U.N.'s special white collar fraud unit, known as the Procurement Task Force, that operated with great success from 2006 to 2008. It found 20 significant corruption schemes, leading to several felony convictions and sanctions against dozens of U.N. vendors.

The General Assembly created it in the wake of the scandal over the $1.8 billion bilked from the oil-for-food program that had been aimed at easing Iraqi suffering under U.N. sanctions.

During two global recruitment rounds in 2008 and 2009, an internal hiring panel selected Appleton from among about 70 applicants as the sole qualified and suitable candidate to serve as permanent head of the investigation division within the U.N.'s Office of Internal Services, or OIOS.

The outgoing head of OIOS, Inga-Britt Ahlenius of Sweden, who stepped down last month after five years, had left the position unfilled from mid-2006. The agency has two other divisions for audits and inspections.

She recalled in a confidential report last month to Ban that severely criticized his leadership how she tried unsuccessfully nine times since late 2008 to fill the job by persuading Ban to hire Appleton.

Ban refused to approve Appleton's hiring as permanent head of the investigation division based on his new policy requiring all senior-level appointments to be chosen from among a field of three qualified candidates that reflect a degree of geographical diversity and include at least one woman.

During the second round, she said, particular emphasis was placed on trying to meet Ban's requirement that there be a candidate, and two women were selected for interviews but did not make the final cut.

Ban and his senior advisers have tried to contain the damage from Ahlenius' leaked 50-page "end-of-assignment" report by telling reporters in a series of news conferences and statements that Ahlenius failed to comply with Ban's new hiring policy.

Consultants found the OIOS' investigation division to be ineffective after the U.N.'s oil-for-food inquiry, in which Appleton, a former supervisory federal prosecutor at a branch office in Connecticut, had served as a special counsel.

Lacking a permanent director, the investigation division has been run by a series of acting directors.

Appleton said in his application that Catherine Pollard, the assistant secretary-general for human resources, made an "inappropriate attempt" to influence the hiring by pushing Ahlenius to interview four more candidates and the sole internal candidate, Michael Dudley, who is the division's current acting director.

Appleton said Dudley's wife, who has a senior-level U.N. post, is a colleague of Pollard's. Dudley e-mailed colleagues within the division in the past week to deny he tried to influence the hiring through his wife's connection to Pollard.

He said in the e-mail obtained by AP that he applied to be the permanent director in 2009 because after seven months as the acting director "it would appear odd if I was not at least considered." He was he was interviewed, but never heard what happened next.

In her report, Ahlenius noted that Pollard wrote Ban's chief of staff to argue for taking a more "flexible approach" toward academic requirements and "suggested that the internal candidate should be considered."

Pollard told reporters last month that the job would have been filled "a lot sooner" if Ahlenius had followed Ban's policy. "It was all about policy, not about a particular personality," Pollard said.

The tribunal to which Appleton applied, which only began operating in July 2009 as part of a new U.N. system of internal justice, was set up by the 192-nation General Assembly to handle grievances by current and former staff members. Its judgments can be appealed to another U.N. tribunal.

Appleton said in his application that Ban and his so-called Senior Review Group that handles senior-level appointments improperly rejected his candidacy by "attempting to politicize the staffing process at OIOS" rather than address the U.N.'s failure to attract more qualified women or more diverse nationalities.

It says Ban and his senior advisers failed to appreciate or follow the U.N.'s hiring rules -- seriously undermining Ahlenius' supposed independence as the U.N.'s undersecretary-general for oversight.